1. Field of the Invention
The present invention relates to a method of removing an organic film adhered to a substrate, enabling the surface of an electronic device substrate or the like to be cleaned, and also relates to an organic film removal apparatus and a resist film removal reagent. In particular the invention relates to the removal of photoresist films used during the processing of semiconductor wafers or liquid crystal substrates. Furthermore, the invention also relates to the removal of organic contaminant films or fine particles from such substrates. In addition, the present invention can also be applied to the removal of more typical organic films such as oil films or paint films from a substrate.
2. Description of the Prior Art
The removal of photoresists used during the ultra fine processing of oxide films or polysilicon films typically employs a method wherein the substrate is immersed in a mixed solution of sulfuric acid (3 or 4 parts by volume) and hydrogen peroxide (1 part by volume) (known as piranha) and heated at 110 to 140° C. for 10 to 20 minutes. In those cases in which a high concentration ion implantation has been performed using a resist mask, the resist itself degenerates and cannot be easily removed using a piranha solution, and consequently ashing with plasma excited oxygen is typically employed. Resists which have suffered surface degeneration following dry etching are also removed in this manner. However, if an entire photoresist is subjected to ashing, organic decomposition residues, fine particles and minute quantities of metal derived from the resist remain, and films of decomposed material also remain on the side walls of channels which have undergone processing. In addition, because the ashing process requires a high energy plasma, the surface of the wafer is also exposed to damage which could harm a semiconductor device. Consequently, ashing is typically performed so that a minute quantity of the resist film remains, and this residual resist is subsequently removed using either piranha treatment, or treatment with an organic solvent such as n-methylpyrolidone (NMP), dimethylsulfoxide (DMSO) or an amine in the case of a metal wiring film process.
Piranha treatment discharges large quantities of sulfuric acid, and similarly treatments which use organic solvents also consume large quantities of solvent, and consequently both types of treatment cause large environmental problems. As a result, resist removal using ozone water has recently been tested. The solubility of ozone in water increases as the temperature is lowered, and if a gas containing a high concentration of ozone (hereafter referred to as ozone gas) is used, then the solubility of ozone in cold water of approximately 0° C. reaches 70 to 100 ppm. However, with this type of ozone water treatment, the stripping rate for a novolak resin based positive resist film used with i-line radiation, which is a widely used configuration in LSI production, is slow, at not more than 0.1 μm/minute, meaning the treatment is not entirely practical. Recently, methods involving treatment with a combination of a high concentration ozone gas and water vapor, and methods involving treatment with a high concentration ozone water utilizing pressurized ozone have also been developed, but the stripping rates with these methods is still slow at approximately 1 μm/minute, and in the case of a substrate comprising a metal wiring film of Cu, W or Mo or the like, damage to the film also becomes a problem.
Regardless of whether piranha treatment or organic solvent treatment is used, from a productivity perspective, the process involves the treatment of a plurality of wafer containing carriers which are inserted in a liquid contained within a cleaning vessel. In the former treatment, hydrogen peroxide decomposes forming water, and the solution gradually becomes diluted, requiring the addition of more hydrogen peroxide, although there is a limit to the amount of additional hydrogen peroxide that can be added. Accordingly, the usable lifespan of the chemical solution in the cleaning vessel is surprisingly short, and large volumes of sulfuric acid need to be discharged, resulting in considerable costs associated with environmental measures. In the case of the latter treatment, repeated use results in an accumulation of dissolved resist within the solvent, which leads to an increase in reverse contamination of the wafer and places a larger load on the rinse solution. Accordingly, the solvent within the cleaning vessel needs to be changed quite regularly. Certainly, neither treatment can be claimed to be economical.
Resists which have undergone strong dry etching or high concentration ion implantation and have suffered considerable degeneration are impossible to remove using conventional wet treatments, and these types of resists are currently removed using ashing methods. However as described above, ashing has a considerable number of associated problems, and also requires a subsequent wet treatment.
In a wet treatment using an organic solvent, metal impurities within the resist migrate into the treatment liquid, and as the treatment liquid is used repeatedly the concentration within the liquid of metal derived from the resist increases. If this metal is a metal with a larger oxide formation enthalpy than silicon, such as iron, zinc or aluminum, then there is a danger of substitution via Si—O linkages occurring at the resist removal surface, resulting in contamination of the surface.
Furthermore, resist removal using organic solvents is used almost exclusively in cases in which the substrate is a metal wiring film. Removal solvents with a strong stripping performance typically contain an amine, and if a rinse with pure water is performed immediately after treatment then strongly alkaline sections are generated, and there is a considerable danger of damage being caused to the metal film of the substrate. Accordingly, the treatment solvent is exchanged with isopropyl alcohol prior to rinsing with pure water, making increases in the organic solvent consumption unavoidable.
A photoresist stripping liquid composition formed from 4-methoxy-1-butanol, 3-methoxy-1-butanol or a mixture of 4- methoxy-1-butanol and 3-methoxy-1-butanol, together with propylene carbonate is disclosed in Japanese Patent Publication No. 2679618 (JP 2679618 B), although no mention is made of the use of only propylene carbonate, and similarly no mention is made of ozone use.
Furthermore, U.S. Pat. No. 5,690,747 discloses a method for removing a photoresist in an ultrasonically agitated solvent comprising (a) 40 to 50 vol % of an aprotic cyclic carbonate ester such as ethylene carbonate, (b) an aprotic polar compound such as ethylene diacetate and ethylene dibutyrate, as well as the solvents N-methyl-2-pyrrolidone and triethanolamine. In addition, the cleaning effect of ethylene carbonate and propylene carbonate on ink and the like has also been reported. However, there have been no reports regarding the use of only ethylene carbonate or propylene carbonate for photoresist removal, nor on their combined use with ozone.